Environment :
Opensuse Leap 15.0 beta with GNOME desktop

Login to desktop as any user. Then check the output of "last" command

Observation :
last command output does not list the display number of the desktop user. It
just displays ":"
Here is a sample output.....

rrm-leap15g:~ # last
root     pts/0        164.99.138.194   Tue Apr 17 11:56   still logged in
rashmi   tty2         tty2             Tue Apr 17 11:56   still logged in
rashmi   :            :                Tue Apr 17 11:56   still logged in
reboot   system boot  4.12.14-lp150.8- Tue Apr 17 09:20   still running

Leap 15.0 with KDE desktop shows the display number properly as ":0" . Here is
the sample output of last command after KDE desktop login..

rrm-leap15k:~ # last
root     pts/0        164.99.138.194   Tue Apr 17 11:55   still logged in
rashmi   tty7         :0               Tue Apr 17 11:54   still logged in
reboot   system boot  4.12.14-lp150.8- Tue Apr 17 09:20   still running